Additive manufacturing method

ABSTRACT

An additive manufacturing method includes manufacturing a workpiece in a manufacturing area by applying metallic powder with a first application device, layer by layer, to a base body. The metallic powder is melted in first regions by a laser beam and solidified. In order to improve the efficiency of selective laser melting, support structures that connect the workpiece to the base body are produced by applying a binder to the powder in second regions with a second application device and solidifying the second regions to produce a powder-binding binder matrix. The support structures are removed from the workpiece after completion thereof by breaking up the binder matrix by degradation with respect to which the workpiece is stable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of GermanApplication No. 102018200010.7, filed on Jan. 2, 2018. The disclosure ofthe above application is incorporated herein by reference.

FIELD

The present disclosure relates to an additive manufacturing method.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

There nowadays exist various methods by means of which, based onconstruction data, three-dimensional models can be produced fromshapeless or shape-neutral materials such as powders (optionally withaddition of a binder) or liquids (which also includes solids that havebeen melted temporarily). These methods are also known by collectiveterms such as “rapid prototyping,” “rapid manufacturing” or “rapidtooling.” It is often the case here that a primary forming step takesplace, in which the starting material is either in liquid form from theoutset or is intermediately liquefied and cures at the intended site. Aknown method in this context is called melt coating (fused depositionmodeling, FDM), in which a workpiece is constructed layer by layer fromthermoplastic material. The plastic is supplied, for example, inpulverulent or strand form, melted and applied in molten form by aprinthead that successively applies individual, generally horizontallayers of the object to be produced.

In addition, there are known methods in which a pulverulent substance,for example a plastic, is applied layer by layer and cured selectivelyby means of a locally applied or printed-on binder. In other methodsagain, for example selective laser sintering (SLS), a powder is applied,for example by means of a coating bar, layer by layer to a baseplate.The powder is selectively heated by means of suitable focused radiation,for example a laser beam, and thereby sintered. After one layer has beenconstructed, the baseplate is lowered slightly and a new layer isapplied. Powders used here may be plastics, ceramic or metals. Theunsintered powder has to be removed after the production process. In asimilar process, selective laser melting (SLM), the amount of energyintroduced by the radiation is so high that the powder is melted inregions and solidifies to form a coherent solid. This method is employedin the case of metallic powders in particular.

In many cases, it is necessary, as well as the actual usable form of theobject, to additionally produce connecting structures or supportstructures that connect the object to the baseplate. These may becolumns, struts, stilts or similar elements that normally runvertically. These serve firstly to assure reliable support in the caseof overhanging shapes and to prevent parts of the object from moving inthe manufacturing process. Secondly, particularly in the case ofmanufacturing methods associated with significant introduction of heat,support structures ensure removal of heat from the object to thebaseplate and prevent the object from warping in the course ofmanufacture as a result of differences in temperature. The input of heatis significantly higher in SLM than in SLS, for example, and for thatreason the support structures are generally absolutely necessary in theformer process for thermal reasons in order to assure controllablemanufacture. At the same time, support structures have to havesufficient thermal conductivity, which can be achieved in that they arelikewise manufactured by SLM from the same metallic powder as theutilizable object.

When the manufacture of the object is complete, it has to be removedfrom the baseplate together with the support structures, for whichpurpose the baseplate generally has to be removed from the manufacturingapparatus. Traditionally, the manual separation of the object from thebaseplate is normally effected by spark erosion (EDM, electricaldischarge machining), more specifically wire erosion, or by mechanicalmeans, for example by means of a saw. Apart from the time taken, adrawback exists in the case of wire erosion that the wire has a tendencyto break on contact with metal powder. After the removal, furtherprocessing of the object is often necessary in order to remove residuesof the support structures. All this means high time demands and anincrease in costs. Owing to the drawback indicated, methods such as SLMare currently unsuitable for economically viable mass production.

U.S. Patent Publication No. 2015/0028523 A1 discloses a method ofadditively manufacturing a workpiece in which support structures areproduced from a material containing a specific polyglycolic acidpolymer. The actual workpiece is produced from a different material. Theadditive manufacture can be effected by extrusion or selective lasersintering or in an electrophotography-based manner. The material of thesupport structures can be dissolved by means of an aqueous, for examplealkaline, solvent.

U.S. Patent Publication No. 2016/0122541 A1 discloses a process forproducing a three-dimensional workpiece by additive manufacture, inwhich, in a heated chamber, a first material for manufacture of theactual workpiece and a second material for manufacture of supportstructures on the workpiece are applied layer by layer selectively inliquid form. The second material comprises a base resin and a dispersionresin dispersed therein. The two resins are mutually immiscible, whichis intended to bring about structural weakening of the supportstructures, which is intended to make it easier to break them away fromthe workpiece.

CN 104786507 A discloses a platform for a 3D printer. The platformcomprises a base body and a coating film applied thereto. The coatingfilm consists of a material that can be dissolved in a suitable solvent.What is envisaged is that a three-dimensional object is constructed onthe platform and, after completion thereof, the coating film isdetached, which detaches the object from the base body which cansubsequently be coated again.

U.S. Patent Publication No. 2016/0185050 A1 discloses a printercartridge for a 3D printer. The cartridge comprises a coil with athermoplastic polymer material that comprises a matrix polymer and twoadditives dispersed therein. The polymer material is supposed to be bothflexible and dimensionally stable. It can be used for additivemanufacture of workpieces and of support structures. For supportstructures, however, it is also possible with preference to use adifferent material that can be dissolved in water or in an aqueousalkaline solution.

As outlined above, the efficiency of the manufacture of workpieces byselective laser melting still has a number of drawbacks. The teachingsof the present disclosure address these drawbacks and assure the thermaland mechanical functionality of the support structures whilesimultaneously enabling more efficient separation thereof from theutilizable workpiece.

SUMMARY

This section provides a general summary of the disclosure and is not acomprehensive disclosure of its full scope or all of its features.

The present disclosure improves the efficiency of a method of selectivelaser melting.

It should be pointed out that the features and measures detailedindividually in the description which follows can be combined with oneanother in any technically meaningful manner and show furtherconfigurations of the present disclosure. The description additionallycharacterizes and specifies the present disclosure, particularly inconnection with the figures.

The present disclosure provides an additive manufacturing method. Themethod can be assigned to the field of rapid prototyping or rapidmanufacturing. As will yet become clear, however, it is suitable notjust for manufacturing of prototypes or individual models, but moreparticularly also for mass production.

In the method of the present disclosure, a workpiece is manufactured by,in a manufacturing area, applying metallic powder by means of a firstapplication device layer by layer to a base body, melting it in regionsby means of a laser beam and solidifying it.

The manufacturing area here is the area in which the actual manufactureor actual construction of the workpiece is effected. Metallic powderhere refers to any pulverulent or particulate material including atleast one metal. It may also be an alloy or a mixture of particles ofdifferent metals. The powder may also contain semimetals or nonmetals,for example as a constituent of an alloy. Useful metals includealuminum, titanium and iron.

The first application device applies one layer of said powder in eachcase across a construction surface. The layer thickness may, forexample, be between 10 μm and 500 μm, although other layer thicknessesare also conceivable. Such an application device may have one or morerelease openings from which the powder exits, for example in thedirection of gravity. In order to enable a smooth and homogeneous layerconstruction, the first application device may including a smoothingdevice, for example a coating bar, brush or blade, which is movedparallel to the construction surface and smooths the surface of thepowder. In general, the construction surface is flat, which means thatit is also possible to refer to a construction plane. The applicationhere is effected layer by layer to a base body, meaning that the firstlayer is applied directly to the base body, and then the further layersare applied successively on top.

In one form, the base body has a flat surface aligned parallel to theconstruction surface. The base body may especially also take the form ofa baseplate or ground plate or have a baseplate. The base body mayinclude, at least predominantly, of a material having high thermalconductivity, for example a metal. After the application of a respectivelayer, the powder is melted in some regions by a laser beam andsubsequently solidifies. In this way, the powder forms a coherent solid.At the same time, the powder of the last added layer is fused to thesolid-state structures of the layer beneath or multiple layers beneath,which establishes coherence of the layers with one another. Depending onthe layer thickness among other factors, it is possible that the laserbeam melts the material down to a depth corresponding to multiple layerthicknesses.

For the purposes of a targeted manufacturing method, the laser beam herenormally acts in accordance with a particular pattern. It could also besaid that a predetermined area is irradiated. It is possible here that,for example, the surface is scanned by a tightly focused laser beam orelse that a particular radiation pattern is projected at the same time.Various scanning patterns are possible; for example, the outline of asurface can first be scanned and then its interior, or vice versa. Thelaser beam is generally aligned with respect to the construction surfacenot by movement of a laser itself but in that a beam generated by thelaser is deflected by means of at least one movable mirror. It will beapparent that the three-dimensional or time-related radiation pattern ofthe laser beam can be controlled in accordance with defined data (e.g.CAM data) of a workpiece to be produced. The irradiated area correspondshere to a (generally flat) cross section of the workpiece. Overall, thismethod can be classified as “selective laser melting” (SLM), or as“application welding.”

During the layer-by-layer application, melting and solidification, thebase body together with the workpiece is normally transported away fromthe construction surface by means of a transport device. A correspondingtransport direction thus runs at an angle, i.e. in a nonparallel manner,to the construction surface. It will be apparent that the transport isnormally intermittent, i.e. discontinuous, in that a layer is appliedwhile the transport device is stationary, and the base body togetherwith the workpiece is transported onward (corresponding to one layerthickness) when the layer has been fully applied. The action of thelaser beam is also normally effected with the base body at rest.However, continuous transport would also be theoretically possible, inwhich case it would be desirable to match the movement of theapplication device and the control of the laser beam to the movement ofthe transport device. The layer-by-layer construction outlined and thesuccessive transporting of the base body together with the workpiece iscontinued until the workpiece is ultimately completed (for example inaccordance with underlying CAM data).

With regard to the alignment of the construction surface and thetransport direction, different configurations are possible, some ofwhich are discussed hereinafter. The base body may in each case have asurface that runs parallel to the construction surface. It is likewisegenerally economic for the angle between the transport direction and theconstruction plane not to be too small, for example at least 30°. Theconstruction surface may run horizontally or else at an angle to thehorizontal, but one that is less than the angle of repose of themetallic powder. The transport direction may run vertically (especiallyin the case of a horizontal construction surface) or else at an angle tothe vertical. If the construction surface runs at an angle to thehorizontal, the transport direction may also be horizontal.

The base body in the method of the present disclosure does not justconstitute a mechanical substrate for the manufacture of the workpiece;instead, it also has an important function for dissipation of heat. Themelting of the powder may cause heating (considerable in some cases) ofthe manufactured workpiece even after the solidification. Good releaseof heat from the workpiece is not possible to surrounding gases orthrough loose powder that adjoins the workpiece, since both arerelatively poor heat conductors. Since, however, the workpiece isconstructed atop the base body, heat can be dissipated to the base body,which inhibits excessive heating of the manufactured workpiece. Thisalso at least substantially inhibits thermal deformation, for examplebending of the workpiece. Without the presence of the base body, theworkpiece could deform so severely that the application of a subsequentpowder layer, for example, would be hindered.

In addition, in the method of the present disclosure, support structuresthat connect the workpiece to the base body are produced by applying abinder to the powder in regions by means of a second application deviceand solidifying it to give a powder-binding binder matrix. The supportstructures here are pure auxiliary structures that are not part of thedesired final shape of the workpiece. They fulfill various functions.For instance, they can serve for mechanical stabilization, for exampleby stabilizing the workpiece during manufacture and any furthertransport and inhibiting tilting of the workpiece. They secondly serveto improve the thermal connection to the base body, such that heat canbe dissipated better from the workpiece. In addition, they are generallyarranged between the base body and the workpiece such that the latter isconnected to the base body only indirectly via the support structures.This makes it possible in a simple manner to separate the workpiece fromthe base body without damage. More particularly, the support structureshere can extend at right angles to the construction surface. They maytake the form of columns, struts, stilts or the like. They can also havean interrupted, for example grid-, mesh- or honeycomb-like, structure.

The binder here is applied specifically and locally to the regions thatare to correspond to support structures. Typically, the binder isapplied in liquid form, which includes the possibility that the binderis solid at ambient temperature and is heated and hence temporarilyliquefied for application to the powder. Normally, the binder, however,is liquid at ambient temperature and, after being applied to the powder,cures owing to a chemical reaction. The expression “the binder” hereincludes the possibility that it is a mixture of two components thatreact with one another and hence bring about the curing process. Itwould also be possible to accelerate or induce the curing in acontrolled manner, for example by means of a UV light source thatirradiates the binder. Thermal acceleration of the curing would also beconceivable, for example in that the laser beam acts on the binder, buta lower energy input should normally be established than in the regionsin which the metal powder is melted. It is especially possible to usebinders that can also withstand high temperatures that can arise incontact with molten metal powder. Examples of these are binders based onfuran resin or phenolic resin. Binders of this kind are also used, forexample, in the 3D printing of sand molds that are used for casting ofmetal parts, and therefore have high thermal stability.

The second application device may have a kind of printhead thateffectively “prints” the binder onto the powder by means of one or morenozzles. The binder is normally applied in such a way that it surroundsthe metallic powder within a thin layer close to the constructionsurface, which means that this powder is incorporated into the curedbinder matrix that forms. It can also be said that the binder matrixbinds or incorporates metallic powder. Such a process can also bereferred to as “binder jetting.” The binder matrix here fulfills twofunctions. It firstly provides the mechanical integrity of the supportstructures. Secondly, dissipation of heat from the workpiece to the basebody takes place through the support structures and hence partly alsothrough the binder matrix. A normally predominant proportion of thesupport structures by volume is taken up by metallic powder. In general,there is contact between adjacent powder particles, albeit only pointcontact, and so a certain proportion of the heat transport is effectedby means of the binder matrix that fills the interstices between theparticles. The binder matrix generally has lower thermal conductivitythan the metal powder enclosed, but its thermal conductivity istypically at least one order of magnitude greater than that of gases.Thus, the thermal conductivity of the support structures issignificantly greater than that of the loose metallic powder where theinterstices between individual particles are filled with gas. In somecases, the melting of metallic powder enables breakdown of the bindermatrix in immediately adjacent areas. In these cases, the connectionbetween the support structures and the workpiece can possibly bemaintained by means of metal particles that have been sintered on, whichgenerate form fitting on the micro-scale and simultaneously providedissipation of heat.

The process steps of the melting of powder and the application of bindercan be conducted in a different sequence in time or else in parallel.These steps are at least largely independent of one another since thepowder is either being melted in a particular part of the applicationarea or is being provided with binder, but not both.

Typically, the method is conducted at least partly within a housing thatcan at least partly encase the first and second application devices, forexample. By means of such a housing, it is firstly possible to inhibitpowder from leaving the actual manufacturing area in an uncontrolledmanner and hence contaminating other areas. More particularly, however,it is possible in a simpler manner within such a housing to conduct atleast parts of the method in an inert gas atmosphere, or in an inertgas-enriched atmosphere that has a distinctly reduced oxygen contentcompared to air, which can inhibit oxidation or even combustion orexplosion of the metallic powder.

The temperature of the base body and the workpiece can optionally becontrolled during or after the manufacture by means of a heatingapparatus and/or a cooling apparatus. Such temperature control canserve, for example, to reduce any intrinsic stresses or to subject theworkpiece to a thermal aftertreatment. In this case, the desired finalshape of the workpiece (i.e. the utilizable part thereof) is fixed onthe base body by means of the support structures and thus safeguardedfrom warping.

After completion of the workpiece, the support structures are removedtherefrom by breaking up the binder matrix by means of degradation withrespect to which the workpiece is stable. Since the support structuresare not part of the actual workpiece, they are removed after completionthereof, which includes the possibility that there are otherintermediate process steps between the completion and the removal. Forremoval of support structures, the binder matrix is broken up; it couldalso be said that it is separated or degraded. The integrity of thebinder matrix is dissolved or destroyed at least in regions, which meansthat the binder matrix breaks down into individual parts that maypossibly also be individual molecules, atoms or ions. Means, which arereferred to here as means of degradation, are used in order to break upthe binder matrix. These means are selected such that the workpiece isstable or insensitive thereto. “Stable” means here that action of thesemeans cannot damage (or permanently alter) the workpiece, or do so atmost to a slight degree which is unimportant in respect of the method.In other words, the fact that the binder matrix has different materialproperties than the actual workpiece is exploited. Since the workpieceis in metallic form, it generally has greater mechanical stability thanthe binder matrix. With regard to other physical or chemical propertiestoo, the workpiece can be more stable or less sensitive than the bindermatrix. The breakup of the binder matrix in many cases means that thesupport structures are not simply removed from the workpiece, but arebroken up in their entirety into parts (possibly individual moleculesetc.).

In the method of the present disclosure, the removal of the supportstructures does not involve any special care or manual activity. This isbecause the means of degradation used cannot damage the workpieceitself, by contrast with the prior art, where the support structuresconsist of the same material as the workpiece, which means that anymeans of removing the support structures can also damage the workpiece.This fact simplifies the removal of the support structures and enablesit to be conducted in a partly or fully automatic manner. Thus, themethod of the present disclosure can be conducted rapidly, efficientlyand inexpensively. In particular, it is also suitable for massproduction, and likewise for the rapid and inexpensive production ofmodels or prototypes. Under some circumstances, the binder matrix canalso be broken up with comparatively low energy expenditure, such that,by comparison with the prior art, an energy saving is also possible. Ineach case, the breakup of the binder matrix is normally found to besimpler than severance of the metallic material of which the workpieceand, in the prior art, the support structures too consist. Nevertheless,the support structures have thermal conductivity by virtue of the bindermatrix and the intercalated metallic powder particles, which means thateffective dissipation of heat from the workpiece to the base body ispossible. A further advantage is that the generation of the supportstructures does not result in any particular introduction of heat, ifany. This contrasts with the prior art, where the support structures aregenerated by melting of powder, which in itself contributes toincreasing the thermal issues.

Although the removal of the support structures from the workpiece iseffected in the inventive manner described above, it is possible thatthe support structures or a portion thereof are separated from the basebody beforehand in a conventional manner. Useful “conventional” methodshere include, for example, cutting-off, sawing or machining and/or othersuitable methods, for example water-jet cutting, laser cutting orerosion.

A great advantage in the method of the present disclosure is that themeans of degradation are chosen such that damage to the workpiecethereby is reduced. In one configuration, the means of degradation alsoact at least on regions of the workpiece. This means that effectivelythe entire arrangement composed of workpiece and support structures (andoptionally the base body) can be exposed to the means of degradationwithout any need for these to be limited to the support structures. Themeans of degradation can thus effectively act over a large area. Asalready set out above, this simplifies the method regime.

In another configuration, the binder matrix is broken up by the actionof a mechanical vibration, especially in the ultrasound range. In otherwords, in this case, the mechanical vibration that the supportstructures (and normally also the workpiece) are induced to create is ameans of degradation. The mechanical vibration, which can also bereferred to as oscillating movement or as a soundwave, producesdifferent mechanical stresses locally in the solids that are affectedthereby, which can lead to fractures. It is possible here firstly toexploit the fact that the material of the binder matrix is moresensitive to other frequencies than the workpiece, and secondly that themetallic workpiece generally has a certain flexibility higher than thatof the binder matrix. Therefore, the binder matrix can also have acertain porosity by contrast with the workpiece that has been molten orwelded in its entirety. The reasons mentioned here for a greatersensitivity of the binder matrix to a vibration, especially a vibrationin the ultrasound range, may be present individually or together, andother reasons are also conceivable as well. In this respect, thedescription of the underlying mechanisms should in no way be interpretedrestrictively. In any case, it is possible, by the action of thevibration, to break up or destroy or to segment the binder matrix, whilethe workpiece remains intact. The vibration can be applied in differentways, for example via surrounding air (or another gas or gas mixture),via a liquid in a vessel into which the support structures andoptionally the workpiece are immersed, or via direct or indirect contactof the workpiece with an ultrasound generator. For example, theworkpiece together with the support structures can be placed in a vesselin direct contact with the ultrasound generator.

In a further form, the binder matrix is dissolved by the action of aliquid solvent. In this case, the liquid solvent should be regarded asthe means of degradation. The composition of the solvent does of coursedepend on the composition of the binder matrix. The solvent here candissolve the binder matrix based on different physical and/or chemicalprocesses, which also includes the possibility that the solvent reactschemically with the binder matrix. The possibility discussed here isadvantageous in that (given a sufficient amount of solvent) the bindermatrix can be removed completely. It will be apparent that the solventhas to be chosen in such a way that it attacks the workpiece only to adegree unimportant in respect of the method, if at all. Normally, thebinder matrix can also be removed completely from the metal powder thathas temporarily been incorporated therein without it being attacked. Thedissolution of the binder matrix may additionally be accelerated by theaction of a mechanical vibration, especially an ultrasound vibration. Itis possible here that the dissolution of the binder matrix and themechanical breakup supplement one another.

Different methods of applying the solvent to the support structures arepossible, such that the binder matrix is dissolved as intended. Moreparticularly, the support structures can be contacted with the solventby at least one of dipping, pouring it over and spraying. In the case ofimmersion, the entire workpiece including the support structures (andoptionally the base body) is immersed into a vessel containing solvent.In the case of pouring-over, the solvent is poured at least over thesupport structures from the top in the manner of a shower, whereas, inthe case of spraying, the solvent can be applied under pressure fromabove, from the side and/or from beneath. While large-area contact withthe solvent can be implemented particularly efficiently by dipping, arespective site on the support structures can be constantly brought intocontact with fresh solvent in the case of pouring-over and in the caseof spraying, which accelerates the dissolving operation. In the case ofdipping, however, it is also possible to keep solvent in motion by meansof stirrers or the like, which likewise accelerates the dissolvingoperation. The methods presented can also be combined with one another,and they can be conducted simultaneously or successively.

With regard to the movement of the two application devices, there aretwo options. In a first configuration, movement of the secondapplication device is coupled to movement of the first applicationdevice. The two application devices here are normally mountedmechanically in a fixed position relative to one another and are movedtogether across the construction surface. This configuration isadvantageous in that the metallic powder can be applied and can bebonded in regions by binders with just one operation. In mechanicalterms, it is desirable here to move just one assembly and to coordinatethe binder release with the corresponding movement. In a secondconfiguration, the movement of the second application device isindependent of the movement of the first application device. This may beadvantageous in that the second application device has to be moved onlyto the regions that actually have to be provided with binder in thecurrent layer. It is possible here for the two application devicesnevertheless to work in parallel in time, meaning that the secondapplication device can already be applying binder while the firstapplication device is still applying metallic powder.

In one aspect, the base body together with the workpiece, aftercompletion thereof, is removed from the manufacturing area andtransported into a processing area in which the support structures areremoved. The transport can of course be effected in an automated mannerby means of grabs, magnets, continuous conveyors or other suitabledevices. The support structures are removed in a removal area arrangedat a distance from the manufacturing area. This in turn means that themanufacturing area becomes free again for manufacture of a furtherworkpiece on a further base body. For this purpose, it is not necessaryto wait until the previously manufactured workpiece has been freed ofthe support structures. Under some circumstances, the time involved forthe transport to the processing area can serve for cooling of the basebody, the support structures and/or the workpiece within an appropriatetime. This may be important, for example, when contact with a solventcould impair either the finished workpiece or the solvent if thetemperature of the workpiece is too high.

The method of the present disclosure serves primarily for removal of thesupport structures in an efficient manner from the manufacturedworkpiece without risking damage to the workpiece. Removal of thesupport structures from the base body could be effected in aconventional manner by sawing, for example, in which case it would bepossible to work with low precision and hence quickly, after which theremoval from the workpiece is effected in the manner according to thepresent disclosure. In addition, however, it is also possible that thesupport structures are also removed from the base body by the action ofthe means of degradation, in which case the base body is stable withrespect to the means of degradation. This is efficiently possible, forexample, when the base body as described above is at least partlymetallic and hence has similar (or identical) properties to the finishedworkpiece.

Especially when the support structures are also being removed from thebase body by the action of the means of degradation, it can subsequentlybe regarded as having been essentially cleaned, which means that reuseis possible. In one development of the method, after the removal of thesupport structures, the base body is reused. Additionally oralternatively, powder bound temporarily within the binder matrix may bereused. Especially when the binder matrix has been dissolved by asolvent, the metallic powder that was bound by the binder can berecovered and reused.

This option is important especially when the powder is, for example, ahigh-value alloy and/or the mass of the support structures iscomparatively high compared to the finished workpiece. Under somecircumstances, it may be desirable to continue the treatment of the basebody or of the powder after the support structures have already beenremoved from the workpiece to a sufficient degree. It is even possiblehere that powder recovered is automatically returned to the firstapplication device. There may be a need here for an intermediateprocessing operation or sorting and sieving of the powder. Automaticrecycling of the base body is also conceivable.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of the production of a workpiece withsupport structures according to the method of the present disclosure;

FIG. 2 shows an enlarged section diagram of a detail from FIG. 1;

FIGS. 3A-3C show a schematic diagram of the removal of supportstructures in a first form of the method of the present disclosure; and

FIGS. 4A-4C show a schematic diagram of the removal of supportstructures in a second form of the method of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

FIG. 1 shows one form of a manufacturing plant 1 that can be used in theadditive manufacturing method of the present disclosure. The diagramhere, as in the other figures too, is highly schematic.

On a lifting device 5 is supported a baseplate 19, on which a workpiece20 is produced in a manufacturing area 1.1 by additive manufacture. Theworkpiece 20 here takes the form of a cog by way of example. By means ofa powder application device 2, metallic powder 4 is applied to thebaseplate 19 layer by layer across a construction surface A. Theconstruction surface A runs parallel here to the surface of thebaseplate 19 and parallel to the horizontal H.

The powder application device 2 may have a kind of nozzle or valve forpowder release and have a smoothing device, for example a coating bar.As indicated by the double-headed arrow, the powder application device 2can be moved parallel to the construction surface A in order todistribute powder 4 across the entire construction surface A. Thebaseplate 19 is adjoined laterally by side walls 6 that inhibit powder 4from trickling off to the side.

When the powder application device 2, connected via a supply conduit 7to a reservoir vessel 8, has applied a layer of metal powder 4, some ofthe powder 4 is selectively melted by means of a laser beam 11, whichcreates a layer of a workpiece 20 to be manufactured. In order toinhibit oxidation or even explosion of the powder 4, the entiremanufacturing plant 1 is disposed within a housing 14 filled with inertgas, or into which inert gas is blown continuously, which keeps theoxygen content low.

The laser beam 11 is generated by a laser 9 and directed by means of apivotable mirror 10 onto an envisaged coordinate point within theconstruction surface A. The activation of the laser 9 and the control ofthe mirror 10 are effected by computer control according to defined CAMdata of the workpiece 20. The lifting device 5 in the present example isoperated intermittently, meaning that it is stopped while a powder layeris being applied and partly melted, and then transports the baseplate 19together with the workpiece 20 in a transport direction T from theconstruction surface A onward by a distance corresponding to theenvisaged layer thickness. The transport direction T in the presentexample runs parallel to the vertical V. It is optionally possible toprovide a cooling device 12 and/or a heating device 13 in order tocontrol the temperature of the manufactured workpiece 20 or thesurrounding powder 4.

The action of the laser beam 11 significantly heats the workpiece 20produced, although the molten powder solidifies again once the action ofthe laser beam 11 has ended. Since effective release of heat is notpossible either to the surrounding powder 4 or to the inert gas, foravoidance of thermal deformations of the workpiece 20, it is desirablefor heat to be released to the baseplate 19. In order to promote this,apart from the workpiece 20, support structures 21 are also generatedthat connect the former to the baseplate 19. These support structures 21firstly stabilize the workpiece 20, but in particular serve for betterdissipation of heat into the baseplate 19. The support structures 21extend transverse to the construction surface A between the baseplate 19and the workpiece 20, such that it is only connected indirectly to thebaseplate 19 via the support structures 21.

The support structures 21 are constructed in that a binder applicationdevice 3 applies a binder to regions of the powder 4. The binderapplication device 3 which may have a nozzle, for example, for releaseof the binder can move parallel to the construction surface A. Thebinder is applied in liquid form, surrounds particles 23 of powder 4 andcures to form a binder matrix 22. FIG. 2 shows a highly enlarged sectiondiagram of a detail of the support structure 21. The thermalconductivity of the respective support structure 21 is determinedfirstly by the metallic particles 23 between which direct conduction ofheat is possible in part owing to contacts, and secondly by the bindermatrix 22 that bridges the interstices between the particles 23, whichgives significantly better conduction of heat than in the case of loosepowder 4. In particular, this is associated with the fact that thethermal conductivity of the binder matrix 22 is typically at least oneorder of magnitude greater than that of the gases within the housing 14.Therefore, effective dissipation of heat is possible by means of thesupport structures 21 even though they are only partly metallic. Thebinder is released through the binder application device 3 undercomputer control according to defined CAM data of the support structures21. In the example shown here, the movement of the binder applicationdevice 3 is independent of that of the powder application device 2.Alternatively, however, it would also be possible to couple the binderapplication device 3 to the powder application device 2. The binderrelease and the melting of the powder 4 by the laser beam 11 can inprinciple be conducted in any sequence successively or else in parallelwithin a layer.

Once the layer-by-layer construction of the workpiece 20 is complete,the baseplate 19 together with the finished workpiece 20 can be removedfrom the lifting device 5. This can be done automatically, as can thetransfer of the baseplate 19 to a processing area 1.2 in which thesupport structures 21 are removed.

FIGS. 3A-3C show the removal of the support structures 21 in a firstvariant. The baseplate 19 together with the workpiece 20 and the supportstructures 21 is introduced here into a tank 15 containing solvent 16.The solvent 16 is selected such that it dissolves the binder matrix 22,but has only a minimal superficial effect at most, if any, on theworkpiece 20, the baseplate 19 and the particles 23 incorporated in thebinder matrix 22. As shown in FIG. 3B, the support structures 21gradually dissolve as a result of breakup of the binder matrix 22 untilthe workpiece 20, just like the baseplate 19, is ultimately released(FIG. 3C). The workpiece can then be removed from the solvent 16 andused (optionally after rinsing the solvent off and/or drying).Correspondingly, it is also possible to reuse the baseplate 19 in themanufacturing plant 1. It is even possible to reuse the particles 23 ofthe powder 4 that were incorporated temporarily in the binder matrix 22.It would be possible here to recover the powder 4 from the solvent 16,for example by filtration, and to recycle it into the reservoir vessel 8(optionally after rinsing and drying).

Although the solvent 16 is being used here in the form of a bath, itcould also be poured or sprayed under pressure onto the supportstructures 21.

FIGS. 4A-4C show an alternative variant for removal of the supportstructures 21, in which the baseplate 19 together with the workpiece 20and the support structures 21 are positioned in a container 17 connectedto an ultrasound generator 18. After activation of the ultrasoundgenerator 18, it generates mechanical vibrations or soundwaves S in theultrasound region that propagate into the support structures 21 firstlyvia the wall of the container 17 and the baseplate 19, and secondly viathe air. The frequency of these soundwaves S is chosen such that theylead to breakup of the binder matrix 22. This gradually breaks down intofragments 24 (see FIG. 4B), until the workpiece 20 and the baseplate 19are ultimately exposed (see FIG. 4C). Under some circumstances, it maybe advantageous to fill the container 17 with a liquid through which thesoundwaves S can propagate. This liquid could even be a solvent 16,which means that the variants shown in FIGS. 3A-3C and in FIGS. 4A-4Ccan advantageously be combined. The mechanical breakup of the bindermatrix 22 and the dissolution thereof can take place in parallel to oneanother.

Unless otherwise expressly indicated herein, all numerical valuesindicating mechanical/thermal properties, compositional percentages,dimensions and/or tolerances, or other characteristics are to beunderstood as modified by the word “about” or “approximately” indescribing the scope of the present disclosure. This modification isdesired for various reasons including industrial practice, manufacturingtechnology, and testing capability.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

As used herein, the phrase at least one of A, B, and C should beconstrued to mean a logical (A OR B OR C), using a non-exclusive logicalOR, and should not be construed to mean “at least one of A, at least oneof B, and at least one of C.

What is claimed is:
 1. An additive manufacturing method comprising:manufacturing a workpiece in a manufacturing area by applying metallicpowder with a first application device layer by layer to a base body,melting the metallic powder in first regions with a laser beam, andsolidifying the metallic powder of the first regions; producing supportstructures that connect the workpiece to the base body by applying abinder to second regions of the metallic powder with a secondapplication device and solidifying the metallic powder of the secondregions such that a powder-binding binder matrix is formed; and removingthe support structures from the workpiece after completion thereof by adegradation process such that the powder-binding binder matrix is brokenup and the workpiece is stable.
 2. The manufacturing method as claimedin claim 1, wherein the degradation process also acts at least onregions of the workpiece.
 3. The manufacturing method as claimed inclaim 1, wherein the powder-binding binder matrix is broken up by amechanical vibration.
 4. The manufacturing method as claimed in claim 3,wherein the mechanical vibration is produced by an ultrasound generator.5. The manufacturing method as claimed in claim 1, wherein thepowder-binding binder matrix is dissolved by action of a liquid solvent.6. The manufacturing method as claimed in claim 5, wherein the supportstructures make contact with the liquid solvent by at least one ofdipping, pouring, and spraying.
 7. The manufacturing method as claimedin claim 1, wherein movement of the second application device is coupledto or independent from a movement of the first application device. 8.The manufacturing method as claimed in claim 1, wherein the base bodyand the workpiece are removed from the manufacturing area aftercompletion thereof and transported into a processing area in which thesupport structures are removed.
 9. The manufacturing method as claimedin claim 1, wherein the support structures are removed from the basebody by the degradation process and the base body remains stable withrespect to the degradation process.
 10. The manufacturing method asclaimed in claim 1 further comprising reusing at least one of the basebody and powder bound intermediately in the powder-binding binder matrixafter the removal of the support structures.
 11. An additivemanufacturing method comprising: applying metallic powder layers to abase body using a first application device; melting first regions of thelayers to produce a workpiece; applying a binder to second regions ofthe layers using a second application device to produce a binder matrix,the binder matrix forming support structures that support the workpiecerelative to the base body; and removing the support structures.
 12. Theadditive manufacturing method as claimed in claim 11, wherein movementof the first application device and second application device areindependent of one another.
 13. The additive manufacturing method asclaimed in claim 11, wherein the first application device and the secondapplication device work in parallel of one another.
 14. The additivemanufacturing method as claimed in claim 11, wherein the supportstructures are removed by a degradation process.
 15. The additivemanufacturing method as claimed in claim 14, wherein the degradationprocess comprises soundwaves generated by an ultrasound generator. 16.The additive manufacturing method as claimed in claim 14, wherein thedegradation process comprises dissolving the support structures in aliquid solvent.
 17. The additive manufacturing method as claimed inclaim 16, wherein the dissolution of the support structures areaccelerated by mechanical vibrations.
 18. The additive manufacturingmethod as claimed in claim 14, wherein at least a portion of theworkpiece is exposed to the degradation process.
 19. The additivemanufacturing method as claimed in claim 11, further comprising reusingat least one of the base body and powder bound intermediately in thebinder matrix after the support structures are removed.
 20. The additivemanufacturing method as claimed in claim 11, further comprising applyinga laser beam to the first regions to melt the first regions of thelayers to produce the workpiece.